Weather pictures & report of August 26 2011

MCS thunderstorm along thermal trough

Synopsis: at 500 hPa, east of a sharp but relaxing trough near the British Isles, our area in a moderate to strong SSW'ly flow of warm and humid potentially unstable air. During the morning passage of a thermal trough advecting a decaying MCS thunderstorm. No severe damage was noted in Belgium (later over Holland it did due to diurnal heating), but at my location it briefly gave some nice structures in the cloudiness. All pictures taken at Kampenhout (central Belgium) with hours in local time (CET).

Surface analysis of August 26 2011 at 0800 CET. Related to a complex depression between England and France, a thermal trough crossing Belgium during the morning - early forenoon. (Source chart: Belgocontrol)

Loop of 8 surface analyses of each hour starting from August 26 at 0500 CET with weather plots showing the thundery outbreak and showers afterwards. (Source: meteocentre.com)

Upper air analysis 500 hPa of August 26 2011 at 0200 CET. A sharp but relaxing upper trough extending from Iceland towards western France. On the eastern flank a ridge over the Balkan. It resulted over our area in a moderate to strong SSW'ly flow. (Source chart: DWD via wetter3)

Upper air analysis 850 hPa of August 26 2011 at 0200 CET. Between the low near Ireland. and anticyclone over western Russia, our area in a moderate S'ly flow of rather warm air. (Source chart: DWD via wetter3)

Loop of forecasted soundings for Brussels of August 26 2011 between 0830-2000 CET. During the morning hours a so called CAP (or inversion) was present below 3000ft. Nevertheless due to passage of a thermal troughline the potentially instability was released during the morning in form of an incoming MCS thunderstorm. Also detectable in the morning is is a pronounced directional windshear but mainly below 1 km height (above the cloudbase level) (Source: RASP)

Another loop of forecasted soundings for a 18 hours period (in steps of three hours) of Brussels from August 26 2011, 0200 CET onwards. Included are some thunderstorms indices: surface based CAPE was during the night barely above 0 J/kg, but the most unstable one went up to a few hundred J/kg (which could be released with a trigger), KI 33-35, TT 47-50, LI -1/-3 = moderate convective potential which may lead to occasional thunderstorms, risk isolated severe. Directional shear was moderate with 194 m²/s², low level shear was 35 kt, deep layer shear 40 kt. Due to the weak to moderate CAPE and moderate shear, multicells (risk MCS with squall-line) with small risk supercells could be expected. (Source: weatheronline.co.uk).

Forecasted vertical profile and surface temperature for Brussels Airport of August 25 from 2000 CET and the following 48 hours. Legend of upper map: green-brown-white is humidity in steps of 10% with darkest green being 90% or more, wind in kt, temperatures each 5°C. Humid air at the begin of the period well towards the upper levels (200 hPa). Furthermore a slight fall of the upper air temperatures (but warmer in lower levels !) during the morning with passage of the thermal trough. Also clearly detectable is a weak to moderate wind shear first 12hours in the lowest 6000ft. (Source: Belgocontrol)

Satellite image of 26/08/2011 at 0410 CET in the infra-red channel with a MCS near Paris moving northwards. (Source sat picture: NOAA and University of Bern).

Satellite image of 26/08/2011 at 0700 CET in the visual RGB channel with a MCS with overshooting top over the south of Belgium. (Source sat picture: Metsat).

26/08/2011 0745-1045 CET. Satellite loop in the visual channel. The mature and gradually decaying MCS thunderstorm overhead Belgium migrated quite quickly towards Holland. More (smaller) cells were formed behind, in the afternoon further exploding to MCS over mid - northeast Holland and northwest Germany. (Source sat picture: Eumetsat via Sat24.com)

Radar loop (rain fall rate in mm) of August 26 2011 between 0615-1145 CET. In the morning a mature (but decaying) MCS on a squall line moved into western and central parts of Belgium. Behind more showers were formed mainly over the eastern parts of Belgium (Source radar picture: Belgocontrol)

Corresponding discharges of August 26 2011 (in two waves) with mainly the central and later eastern parts of Belgium. Holland was affected more intense, especially on the showers in the afternoon over the eastern parts (Source lightning picture: Buienradar)

Metars of Brussels Airport (EBBR) (hours in UTC). Translation: copy paste each obs via metar-decoder

EBBR 260420Z 11010KT 080V140 8000 NSC 18/16 Q1002 NOSIG

EBBR 260450Z 11011KT 8000 FEW014 19/17 Q1002 BECMG FM0600 VRB23G40KT 1500 +TSRA BKN008 BKN014CB

EBBR 260520Z 14008KT 8000 FEW014CB 18/17 Q1002 BECMG FM0600 VRB23G40KT 1500 +TSRA BKN008 BKN014CB

EBBR 260550Z /////KT 7000 R25R///// TSRA FEW014CB 17/16 Q1004 NOSIG

EBBR 260620Z 16004KT 9999 R25R///// FEW014TCU 18/17 Q1003 RETSRA NOSIG

EBBR 260650Z 13006KT 9999 R25R///// FEW020TCU 19/17 Q1002 NOSIG

EBBR 260720Z 16007KT 130V210 9999 R25R///// FEW020TCU 19/17 Q1002 TEMPO VRB20G45KT 2500 TSRA BKN014CB

EBBR 260750Z 23009KT 7000 SHRA FEW020CB 19/17 Q1002 TEMPO VRB20G35KT 2500 TSRA BKN014CB

EBBR 260820Z 23006KT 9999 FEW020CB 18/16 Q1004 RESHRA TEMPO 4000 SHRA BKN014CB

EBBR 260850Z 14004KT 110V190 9999 -SHRA FEW025CB 18/16 Q1003 NOSIG

Metars of Beauvechain (EBBE) (hours in UTC)

EBBE 260414Z 09008KT 4000 BR FEW100 BKN220 17/17 Q1003 GRN GRN TEMPO YLO

EBBE 260425Z 09009KT 4000 BR BKN230 17/17 Q1003 GRN GRN TEMPO YLO

EBBE 260525Z 11007KT 5000 BR BKN145 BKN240 18/17 Q1002 WHT GRN TEMPO YLO

EBBE 260538Z 14005KT 4000 -TS FEW015CB SCT130 BKN145 18/17 Q1003 GRN YLO TEMPO AMB

EBBE 260625Z 24006KT 9999 FEW013 SCT024 BKN035 18/17 Q1004 RETS WHT BLU TEMPO GRN

EBBE 260704Z VRB02KT 9999 FEW024 BKN040 18/17 Q1003 BLU WHT TEMPO GRN

EBBE 260725Z 14005KT 9999 FEW024 BKN040 OVC049 18/16 Q1003 BLU WHT TEMPO GRN

EBBE 260746Z 14006KT 9999 FEW012 BKN040 19/17 Q1003 BLU WHT TEMPO YLO

EBBE 260801Z 24009KT 5000 -SHRA SCT010 BKN025 19/18 Q1004 GRN WHT TEMPO YLO

EBBE 260806Z 25010KT 3000 TSRA SCT010CB BKN025 18/18 Q1004 YLO GRN BECMG WHT

EBBE 260818Z 23007KT 5000 -TSRA SCT010CB BKN025 18/18 Q1004 GRN WHT TEMPO GRN

EBBE 260825Z 23005KT 9999 FEW010CB SCT020 BKN040 18/18 Q1004 RETS WHT BLU TEMPO GRN

26/08/2011 0743 N. On passage of the squall-line there was presumable a weak shelf cloud present. When ready to take pictures it already was overhead giving this nice whales mouth effect.

26/08/2011 0744 S. Opposite side also the whales mouth effect.

26/08/2011 0750 N. Some near by vertical strikes were observed, only one could be taken on the edge of the frame. Its distance was less than 2 km, according SAFIR even right in my street a few houses away but this was certainly not the case.